1. Field of the Invention
The present invention relates generally to die bonders for die-bonding a semiconductor chip formed in a wafer to a lead frame and methods of producing a semiconductor device using the die bonder, and particularly to die bonders allowing increased yields of semiconductor devices and methods of producing a semiconductor device using the die bonder.
2. Description of the Background Art
FIG. 10 shows an appearance of a wafer marked with a bad mark. Conventionally, semiconductor chips formed in wafers are all tested by a tester apparatus wafer by wafer. Then, as shown in FIG. 10, any defective semiconductor chips are marked with a bad mark 34. Then a die bonder used to die-bond a semiconductor chip for example to a lead frame recognizes bad mark 34 on a wafer to determine whether the chip passes or fails. Only conforming semiconductor chips are thus selected and die-bonded to the lead frame.
Whether a semiconductor chip passes or fails is determined from a value of a characteristic of the chip and the appearance of the chip. This decision is made by a tester conducting an electrical test and a tester conducting an appearance test and if the chip is defective it is marked by bad mark 34. Rather than using the appearance tester, a visual inspection may alternatively be conducted in another step and products thus found to be defective in appearance may be marked by bad mark 34 manually.
While semiconductor chips have different sizes, such as 1 mm square, 2 mm square, 3 mm square and 4 mm square, bad mark 34 has a size for example of approximately 0.5 to 0.6 mm xcfx86 to consider the tester""s performance. If bad mark 34 is manually provided the mark would vary in size.
When a die bonder is used to detect bad mark 34 provided on a wafer, the wafer""s surface condition, the size of bad mark 34 on the wafer, a reflection of light from the wafer, and the like vary for each lot of wafers. Accordingly to recognize a bad mark on a wafer a device included in the die bonder to recognize the bad mark needs to be adjusted for each lot of wafers, which is inefficient. Furthermore, the die bonder that has been adjusted still can be affected by a condition of a surface of a wafer and erroneously recognize a bad mark during production and a recognition error can thus be made.
Among semiconductor devices there are those called high rank products having a superior characteristic and those called ordinary products having a characteristic inferior to the high rank products. To produce a high rank product, a costly wafer corresponding to the high rank product needs to be used or a less costly wafer corresponding to an ordinary product having a characteristic wider in range than the high rank product is used to produce semiconductor devices and after the devices are completed only those having the characteristic corresponding to the high rank product need to be selected. The process using the costly wafer requires increased production cost and the process including screening semiconductor devices to select high rank products from provides reduced yields.
The present invention has been made to resolve the above disadvantages.
One object of the present invention is to provide a die bonder which can eliminate the necessity of marking a wafer with a bad mark and still provide increased yields of semiconductor devices having a superior characteristic (high rank products).
Another object of the present invention is to provide a semiconductor device production method which can eliminate the necessity of marking a wafer with a bad mark and still provide increased yields of semiconductor devices having a superior characteristic.
To achieve the above objects the present invention in one aspect provides a die bonder including: a storage storing inspection data of each of a plurality of semiconductor chips formed in a wafer and a position of each of the plurality of semiconductor chips as seen in the wafer, the inspection data being correlated with the position; a wafer screening portion referring to the inspection data of the semiconductor chips in the storage to screen a plurality of wafers to select a wafer; and a die-bonding portion die-bonding to a frame of a semiconductor device having a characteristic of a first level a semiconductor chip formed in a wafer selected by the wafer screening portion.
In accordance with the present invention semiconductor chip inspection data stored in the storage can be referred to to screen wafers and a semiconductor chip formed in a wafer thus selected can be die-bonded to a lead frame of a semiconductor device. This can eliminate the necessity of marking a wafer with a bad mark at the inspection step and requiring the die bonder to recognize the bad mark. Furthermore since a wafer selected in accordance with the semiconductor chip inspection data can be used to die-bond a semiconductor chip to a lead frame of a semiconductor device the die bonder can provide increased yields of semiconductor devices.
Preferably the wafer screening portion selects a wafer including no less than a prescribed number of semiconductor chips having the inspection data falling within a range of a first predetermined reference value.
In accordance with the present invention a wafer is selected when it includes no less than a prescribed number of chips having inspection data falling within the range of a first predetermined reference value. As a semiconductor device has a characteristic affected by a semiconductor chip to be mounted, selecting a wafer having no less than the prescribed number of chips having inspection data falling within the range of the first predetermined reference value allows the die bonder to produce from a single wafer at least a prescribed number of semiconductor devices having a characteristic having a value exceeding a predetermined value.
The present invention in another aspect provides a die bonder including: a storage storing inspection data of each of a plurality of semiconductor chips formed in a wafer and a position of each of the plurality of semiconductor chips as seen in the wafer, the inspection data being correlated with the position; a semiconductor chip screening portion referring to the inspection data of the semiconductor chips in the storage to screen a plurality of semiconductor chips to select a semiconductor chip; and a die-bonding portion die-bonding to a frame of a semiconductor device a semiconductor chip selected by the semiconductor chip screening portion.
In accordance with the present invention a semiconductor chip selected in accordance with inspection data can be die-bonded to a lead frame of a semiconductor device. As a semiconductor device has a characteristic affected by a semiconductor chip to be mounted, die-bonding a semiconductor chip selected in accordance with inspection data to a lead frame of a semiconductor device allows the die bonder to provide increased yields of semiconductor devices.
Preferably the semiconductor chip screening portion selects a semiconductor chip having the inspection data falling within a first range and the die-bonding portion die-bonds the selected semiconductor chip to a frame of a semiconductor device having a characteristic of a first level.
In accordance with the present invention a chip having inspection data falling within the first range can be selected and die-bonded to a frame of a semiconductor device having a characteristic of a first level. The die bonder can thus provide increased yields of semiconductor devices having the characteristic of the first level.
The present invention in still another aspect provides a method of producing a semiconductor device, including the steps of: inspecting each of a plurality of semiconductor chips formed in a wafer; correlating and storing inspection data obtained at the step of inspecting and a position of each of the semiconductor chips as seen on the wafer; screening the semiconductor chips in accordance with the stored inspection data of the semiconductor chips to select a semiconductor chip; and die-bonding the selected semiconductor chip to a frame of a semiconductor device.
In accordance with the present invention, before a semiconductor chip is die-bonded to a lead frame of a semiconductor device the chip can be inspected and inspection data thus obtained can be used to screen the chip. If the chip is selected it is die-bonded to a lead frame of a semiconductor device. As a semiconductor device has a characteristic affected by a semiconductor chip to be mounted, using the inspection data to select a semiconductor chip and die-bonding the selected chip to a lead frame of a semiconductor device allows the semiconductor device production method to provide increased yields of semiconductor devices.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.